Bernie Sanders unloads on Hillary Clinton over her support from Henry Kissinger

Bernie Sanders and Hillary Clinton.
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Sen. Bernie Sanders (I-Vermont) launched an attack on Hillary Clinton over her relationship with controversial former US Secretary of State Henry Kissinger.

Sanders pointed out that Clinton has touted her support from Kissinger on the campaign trail — and then scorned him as "one of the most destructive secretaries of state in the modern history of the country."

"In the last debate, and I believe in her book … she talked about getting the approval or support or the mentoring of Henry Kissinger," Sanders said. "Now I find it rather amazing, because I happen to believe that Henry Kissinger was one of the most destructive secretaries of state in the modern history of the country. I am proud to say that Henry Kissinger is not my friend. I will not take advice from Henry Kissinger."

Clinton shot back: "Well, I know journalists have asked who you do listen to on foreign policy, and we have yet to know who that is."

"That's fine, that's fine. I listen to a wide variety of voices that have expertise in various areas," she said. "I think it is fair to say, whatever the complaints that you want to make about him are, that with respect to China, one of the most challenging relationships we had, his opening up China and his ongoing relationships with the leaders of China is an incredibly useful relationship for the United States of America."

She also clarified that she doesn't agree with all of the decisions Kissinger made during his tenure as secretary of state, a position that Clinton also held from 2009-13.

"Yes, people we may disagree with on a number of things may have some insight, may have some relationships that are important for the president to understand in order to best protect the United States," Clinton said.

The attack over Clinton's relationship with Kissinger appears to have been in the works. Right after Sanders' attack, the Sanders campaign sent out a memo about dangers of Clinton's support from Kissinger.

"Hillary Clinton claims that she is a 'true progressive,' and yet she has aligned herself with one of the most conservative, and controversial, members of the political establishment in US history," the memo stated.

The memo then went on to list 13 of Kissinger's "most egregious acts while in office."

Later on in the debate, in response to a question about which leaders would most influence each candidate's foreign policy, Sanders named former British Prime Minister Winston Churchill, who many view as a hawkish aggressor.